This invention relates generally to methods for depositing particles from liquid suspensions of the same. More particularly, it relates to a method for depositing liquid-suspended particles to form a surface layer on an article having interconnected pores. The invention is a result of a contract with the United States Department of Energy.
The invention was made in the course of experiments directed toward finding a reproducible method for depositing uniform coatings of graphite on the exterior surfaces of relatively fragile fibrous-carbon rings. (See U.S. Pat. No. 3,577,344, "Fibrous Thermal Insulation and Method of Making the Same", issued on May 4, 1971). The typical ring comprised more than 90% air by volume and was characterized by a very large number of interconnected small pores. The intention was to provide the fibrous rings with a smooth external coating of graphite while minimizing impregnation of interior pores. Conventional spraying and brushing techniques were tested but were found unsatisfactory for one or more of the following reasons: insufficient deposition, non-uniform deposition, non-reproducibility, or damage to the rings. In another test, a liquid suspension of colloidal graphite was pumped through the wall of a typical ring. This resulted in some impregnation of the ring, but very little graphite was deposited on its external surface.